DECLARE @SQL VARCHAR(8000) 

SELECT @SQL=COALESCE(@SQL,'')+'Kill '+CAST(spid AS VARCHAR(10))+ '; '  
FROM sys.sysprocesses  
WHERE DBID=DB_ID('AdventureWorks') 

PRINT @SQL --EXEC(@SQL) Replace the print statement with exec to execute

http://www.mssqltips.com/sqlservertip/1521/the-many-uses-of-coalesce-in-sql-server/

If you have ever tried to restore a database and could not obtain exclusive access, you know how useful this can be.

kill all the transactions in a database

SQL